Equatorial plasma bubbles with enhanced ion and electron temperatures

Abstract

[1] While the ion and electron temperatures inside equatorial plasma bubbles (EPBs) are normally lower than those in an ambient plasma, bubbles with enhanced temperatures (BETs) are found occasionally in the topside ionosphere. Here we report the characteristics of BETs identified from observations of the first Republic of China Satellite (ROCSAT-1), the first Korea Multi-purpose Satellite (KOMPSAT-1), and the Defense Meteorological Satellite Program (DMSP) F15 during the solar maximum period between 2000 and 2001. The oxygen ion fraction inside the BETs, which was no lower than that of the ambient ionosphere, was similar to the case of ordinary low-temperature EPBs. These observations indicate that the BETs and low-temperature EPBs detected on the topside were produced by the upward drift of low-density plasma from lower altitudes. The feature that distinguishes BETs from normal EPBs is the occurrence of an unusually fast poleward field-aligned plasma flow relative to the ambient plasma. The BETs occurred preferentially around geomagnetic latitudes of 10°in the summer hemisphere, where the ambient ion and electron temperatures are lower than those in the conjugate winter hemisphere. The occurrence of BETs did not show any notable dependence on geomagnetic activities. The characteristics of the BETs suggest that the BETs were produced by adiabatic plasma heating associated with a fast poleward oxygen ion transport along magnetic flux tubes.

The characteristics of field-aligned currents associated with equatorial plasma bubbles as observed by the CHAMP satellite

“…Kil and Heelis, 1998;Huang et al, 2001;Park et al, 2005;Stolle et al, 2006). Electron temperatures inside EPBs are generally lower than that of the ambient (Oyama et al, 1988), but sometimes higher due to adiabatic compression along the flux tube (Su et al, 2003;Park et al, 2008). In spectral respect EPBs are self-similar steepened structures when the ion-neutral collision frequency is high (Hysell et al, 1994), but similar to Kolmogorov turbulence in collisionless environments (Shume and Hysell, 2004).…”

“…The resulting "residual" field is then transformed into the mean-field-aligned (MFA) coordinate system, where the z-component, "parallel," is along the mean field, the y-component, "zonal," is perpendicular to the magnetic meridian and is pointing to the east, and the x-component, "meridional," completes the triad and points outward. A similar approach was used in Stolle et al (2006), Park et al (2008), and Park et al (2009). Remaining largescale variations of order 10 nT, which are not properly allowed for by POMME4, are further eliminated with a 91-point (∼700 km) median filter in Sects.…”

Density enhancements associated with equatorial spread <I>F</I>

“…We have found that ESF ion dynamics lead to specific compositional and thermal signatures. ESF-plume temperatures (Oyama et al, 1988;Park et al, 2008a) have been explained in some detail by Huba et al (2009a), but many aspects of simulated ESF plume density structures have not.…”

Traveling ionospheric disturbances and their relations to storm‐enhanced density features and plasma density irregularities in the local evening and nighttime hours of the Halloween superstorms of 29–31 October 2003

“…When the zonal E field is eastward directed and thus the E × B drift is upward directed, bottomside bubbles may rise in altitude into the topside ionosphere around the equator. However, away from the equator, topside bubbles may drift downward and propagate poleward along the magnetic field lines [ Park et al , 2008]. Topside ionospheric depletions are specifically called bubbles as the conditions in the topside ionosphere are stable for R‐T modes, and therefore, plasma depletions found there must have originated in the bottomside and drifted up into the topside by buoyancy mechanisms [ Krause et al , 2005].…”